1. Field of the Invention
This invention relates to a novel photographic reproduction process, a photosensitive composition and photosensitive element to be used in the process and to apparatus used in practicing the photographic process. More specifically, the present invention relates to a dry physical development photographic process based on a photosensitive composition which includes a photopolymerizable monomer and a thermochromic substance and to the apparatus for carrying out this process.
2. Prior Art
Most photographic processes that allow production of a permanent image are based on photochemical reactions and require use of liquid chemical agents to develop and fix the image. This is the case especially in the conventional silver process in which a silver halide is used as the photosensitive compound.
As a result of the need to have recourse to liquid agents to develop and fix the silver image these baths will become depleted of their active ingredients, or modify in the course of use; this necessitates frequent changing or supplementing of the baths. This drawback is particularly bothersome in automatic facilities, because there has to be constant monitoring and maintenance of these baths. This drawback is especially troublsome, for example, in facilities that deliver identification photos at a moderate cost. It would thus be desirable to have a photographic process that would avoid the use of liquid agents for development and fixing.
There are photographic processes that do not use silver, namely processes that are based on a photopolymerization reaction. Such processes would allow high sensitivity, of the order of ASA 200. Theoretically they could be substituted for the conventional silver process, but they do not directly produce a visible image, and require a developing operation. It is this that has thus far limited their use.
For example, British Patent 905,182 discloses coatings capable of being converted to imagewise photopolymerized resists from a compound containing the ##EQU1## in which an oil-soluble colorant such as dye or pigment is dispersed. The light sensitive material is exposed under a pattern to white-light. Where the light passes through the pattern, photopolymerization of the light-sensitized material takes place to produce hydrophobic areas. The light-sensitized material is then subjected to the action of a hydrophilic solvent such as water, alcohol or the like for a matter of seconds to remove the unexposed unpolymerized areas.
British Patent 980,286 discloses a photographic element comprising a support having coated thereon a photosensitive layer comprising a photographic colloid carrier having dispersed therein a normally liquid or solid dispersible monomer containing the grouping CH.sub.2 =C=, a substantially water insoluble carboxylic aliphatic acid having from 10 to 27 carbon atoms inclusive and a light-sensitive ferric salt. The aforesaid light-sensitive element is then exposed to visible light through a pattern or a suitable optical image, the exposed element then developed by contacting with a per compound containing the grouping --O--O-- whereby polymerization takes place in those areas of the element which were exposed. In the unexposed portions of the plate, there is no reaction, and the monomer remains unpolymerized. The residual unpolymerized portions of the coating are removed by washing which leaves intact the polymeric resist image corresponding to the exposed areas. The washed plate is next inbibed or steeped in a solution of basic dye which has a strong affinity or substantivity for the polymeric image containing the dispersed higher fatty acid.
U.S. Pat. No. 2,760,863 discloses a process for preparing relief images for direct use as printing plates "by exposing with actinic light through a process transparency . . . a photopolymerizable layer or stratum comprising a polymerizable ethylenically unsaturated composition (e.g. a compound or mixture of compounds) having intimately dispersed therethrough an addition polymerization initiator activatable by actinic light, [the] layer or stratum being superposed on a suitable adherent support, i.e., adherent to the photopolymerized composition, until substantially complete polymerization takes place in the exposed areas and substantially no polymerization takes place in the non-exposed areas, and essentially completely removing the layer, e.g. the unpolymerized composition together with any admixed material, in [the] non-exposed areas."
It can be seen that the conventional reproduction processes based on a photopolymerization reaction still require difficult and uneconomical development and fixing steps.